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powerpc/mm: Preserve CFAR value on SLB miss caused by access to bogus address

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Currently, if userspace or the kernel accesses a completely bogus address,
for example with any of bits 46-59 set, we first take an SLB miss interrupt,
install a corresponding SLB entry with VSID 0, retry the instruction, then
take a DSI/ISI interrupt because there is no HPT entry mapping the address.
However, by the time of the second interrupt, the Come-From Address Register
(CFAR) has been overwritten by the rfid instruction at the end of the SLB
miss interrupt handler.  Since bogus accesses can often be caused by a
function return after the stack has been overwritten, the CFAR value would
be very useful as it could indicate which function it was whose return had
led to the bogus address.

This patch adds code to create a full exception frame in the SLB miss handler
in the case of a bogus address, rather than inserting an SLB entry with a
zero VSID field.  Then we call a new slb_miss_bad_addr() function in C code,
which delivers a signal for a user access or creates an oops for a kernel
access.  In the latter case the oops message will show the CFAR value at the
time of the access.

In the case of the radix MMU, a segment miss interrupt indicates an access
outside the ranges mapped by the page tables.  Previously this was handled
by the code for an unrecoverable SLB miss (one with MSR[RI] = 0), which is
not really correct.  With this patch, we now handle these interrupts with
slb_miss_bad_addr(), which is much more consistent.

Signed-off-by: Paul Mackerras <paulus@ozlabs.org>
Reviewed-by: Aneesh Kumar K.V <aneesh.kumar@linux.vnet.ibm.com>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
This commit is contained in:
Paul Mackerras 2016-09-02 21:49:21 +10:00 committed by Michael Ellerman
parent b42d9023a3
commit f0f558b131
3 changed files with 49 additions and 11 deletions
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40
arch/powerpc/kernel/exceptions-64s.S
View File

@ -175,6 +175,7 @@ data_access_slb_pSeries:
std r3,PACA_EXSLB+EX_R3(r13)
mfspr r3,SPRN_DAR
mfspr r12,SPRN_SRR1
crset 4*cr6+eq
#ifndef CONFIG_RELOCATABLE
b slb_miss_realmode
#else
@ -201,6 +202,7 @@ instruction_access_slb_pSeries:
std r3,PACA_EXSLB+EX_R3(r13)
mfspr r3,SPRN_SRR0 /* SRR0 is faulting address */
mfspr r12,SPRN_SRR1
crclr 4*cr6+eq
#ifndef CONFIG_RELOCATABLE
b slb_miss_realmode
#else
@ -783,6 +785,7 @@ data_access_slb_relon_pSeries:
std r3,PACA_EXSLB+EX_R3(r13)
mfspr r3,SPRN_DAR
mfspr r12,SPRN_SRR1
crset 4*cr6+eq
#ifndef CONFIG_RELOCATABLE
b slb_miss_realmode
#else
@ -808,6 +811,7 @@ instruction_access_slb_relon_pSeries:
std r3,PACA_EXSLB+EX_R3(r13)
mfspr r3,SPRN_SRR0 /* SRR0 is faulting address */
mfspr r12,SPRN_SRR1
crclr 4*cr6+eq
#ifndef CONFIG_RELOCATABLE
b slb_miss_realmode
#else
@ -1408,6 +1412,7 @@ unrecover_mce:
* r3 has the faulting address
* r9 - r13 are saved in paca->exslb.
* r3 is saved in paca->slb_r3
* cr6.eq is set for a D-SLB miss, clear for a I-SLB miss
* We assume we aren't going to take any exceptions during this procedure.
*/
slb_miss_realmode:
@ -1418,29 +1423,31 @@ slb_miss_realmode:
stw r9,PACA_EXSLB+EX_CCR(r13) /* save CR in exc. frame */
std r10,PACA_EXSLB+EX_LR(r13) /* save LR */
std r3,PACA_EXSLB+EX_DAR(r13)
crset 4*cr0+eq
#ifdef CONFIG_PPC_STD_MMU_64
BEGIN_MMU_FTR_SECTION
bl slb_allocate_realmode
END_MMU_FTR_SECTION_IFCLR(MMU_FTR_TYPE_RADIX)
#endif
/* All done -- return from exception. */
ld r10,PACA_EXSLB+EX_LR(r13)
ld r3,PACA_EXSLB+EX_R3(r13)
lwz r9,PACA_EXSLB+EX_CCR(r13) /* get saved CR */
mtlr r10
beq 8f /* if bad address, make full stack frame */
andi. r10,r12,MSR_RI /* check for unrecoverable exception */
BEGIN_MMU_FTR_SECTION
beq- 2f
FTR_SECTION_ELSE
b 2f
ALT_MMU_FTR_SECTION_END_IFCLR(MMU_FTR_TYPE_RADIX)
/* All done -- return from exception. */
.machine push
.machine "power4"
mtcrf 0x80,r9
mtcrf 0x02,r9 /* I/D indication is in cr6 */
mtcrf 0x01,r9 /* slb_allocate uses cr0 and cr7 */
.machine pop
@ -1470,6 +1477,27 @@ unrecov_slb:
bl unrecoverable_exception
b 1b
8: mfspr r11,SPRN_SRR0
ld r10,PACAKBASE(r13)
LOAD_HANDLER(r10,bad_addr_slb)
mtspr SPRN_SRR0,r10
ld r10,PACAKMSR(r13)
mtspr SPRN_SRR1,r10
rfid
b .
bad_addr_slb:
EXCEPTION_PROLOG_COMMON(0x380, PACA_EXSLB)
RECONCILE_IRQ_STATE(r10, r11)
ld r3, PACA_EXSLB+EX_DAR(r13)
std r3, _DAR(r1)
beq cr6, 2f
li r10, 0x480 /* fix trap number for I-SLB miss */
std r10, _TRAP(r1)
2: bl save_nvgprs
addi r3, r1, STACK_FRAME_OVERHEAD
bl slb_miss_bad_addr
b ret_from_except
#ifdef CONFIG_PPC_970_NAP
power4_fixup_nap:

12
arch/powerpc/kernel/traps.c
View File

@ -1310,6 +1310,18 @@ void alignment_exception(struct pt_regs *regs)
exception_exit(prev_state);
}
void slb_miss_bad_addr(struct pt_regs *regs)
{
enum ctx_state prev_state = exception_enter();
if (user_mode(regs))
_exception(SIGSEGV, regs, SEGV_BNDERR, regs->dar);
else
bad_page_fault(regs, regs->dar, SIGSEGV);
exception_exit(prev_state);
}
void StackOverflow(struct pt_regs *regs)
{
printk(KERN_CRIT "Kernel stack overflow in process %p, r1=%lx\n",

8
arch/powerpc/mm/slb_low.S
View File

@ -173,11 +173,9 @@ BEGIN_FTR_SECTION
END_MMU_FTR_SECTION_IFSET(MMU_FTR_1T_SEGMENT)
b slb_finish_load
8: /* invalid EA */
li r10,0 /* BAD_VSID */
li r9,0 /* BAD_VSID */
li r11,SLB_VSID_USER /* flags don't much matter */
b slb_finish_load
8: /* invalid EA - return an error indication */
crset 4*cr0+eq /* indicate failure */
blr
/*
* Finish loading of an SLB entry and return